diff --git a/horizon/test/unit/workflows/test_workflows.py b/horizon/test/unit/workflows/test_workflows.py
index 8dd0c85bde..04b907b576 100644
--- a/horizon/test/unit/workflows/test_workflows.py
+++ b/horizon/test/unit/workflows/test_workflows.py
@@ -18,6 +18,7 @@ import mock
 
 import six
 
+from horizon import base
 from horizon import exceptions
 from horizon.test import helpers as test
 from horizon import workflows
@@ -335,6 +336,10 @@ class WorkflowsTests(test.TestCase):
                                   '<TestStepThree: test_action_three>',
                                   '<TestStepTwo: test_action_two>'])
 
+    def test_workflow_unregister_unexisting_workflow(self):
+        with self.assertRaises(base.NotRegistered):
+            TestWorkflow.unregister(TestDisabledStep)
+
     def test_workflow_render(self):
         TestWorkflow.register(TestStepThree)
         req = self.factory.get("/foo")
diff --git a/horizon/workflows/base.py b/horizon/workflows/base.py
index a27d73dc9e..1f814e1123 100644
--- a/horizon/workflows/base.py
+++ b/horizon/workflows/base.py
@@ -810,7 +810,7 @@ class Workflow(html.HTMLElement):
         """Unregisters a :class:`~horizon.workflows.Step` from the workflow."""
         try:
             cls._cls_registry.remove(step_class)
-        except KeyError:
+        except ValueError:
             raise base.NotRegistered('%s is not registered' % cls)
         return cls._unregister(step_class)